The present invention relates generally to light sources, and more particularly to a high efficiency light source in the form of an optical magnetron.
Magnetrons are well known in the art. Magnetrons have long served as highly efficient sources of microwave energy. For example, magnetrons are commonly employed in microwave ovens to generate sufficient microwave energy for heating and cooking various foods. The use of magnetrons is desirable in that they operate with high efficiency, thus avoiding high costs associated with excess power consumption, heat dissipation, etc.
Microwave magnetrons employ a constant magnetic field to produce a rotating electron space charge. The space charge interacts with a plurality of microwave resonant cavities to generate microwave radiation. Heretofore, magnetrons have been generally limited to maximum operating frequencies below about 100 Gigahertz (Ghz). Higher frequency operation previously has not been considered practical for perhaps a variety of reasons. For example, extremely high magnetic fields would be required in order to scale a magnetron to very small dimensions. In addition, there would be considerable difficulty in fabricating very small microwave resonators. Such problems previously have made higher frequency magnetrons improbable and impractical.
In view of the aforementioned shortcomings associated with conventional microwave magnetrons, there exists a strong need for a magnetron which is suitable as a practical matter for operating at frequencies which exceed 100 Gigahertz (i.e., an optical magnetron). For example, there is a strong need in the art for an optical source capable of producing light with higher efficiency as compared to conventional types of light sources (e.g., incandescent, flourescent, laser, etc.). Such an optical source would have utility in a variety of applications including, but not limited to, optical communications, commercial and industrial lighting, manufacturing, etc.
The present invention provides an optical magnetron suitable for operating at frequencies heretofore not possible with conventional magnetrons. The optical magnetron of the present invention is capable of producing high efficiency, high power electromagnetic energy at frequencies within the infrared and visible light bands, and which may extend beyond into higher frequency bands such as ultraviolet, x-ray, etc. As a result, the optical magnetron of the present invention may serve as a light source in a variety of applications such as long distance optical communications, commercial and industrial lighting, manufacturing, etc.
The optical magnetron of the present invention is advantageous as it does not require extremely high magnetic fields. Rather, the optical magnetron preferably uses a magnetic field of more reasonable strength, and more preferably a magnetic field obtained from permanent magnets. The magnetic field strength determines the radius of rotation of the electron space charge within the interaction region between the cathode and the anode (also referred to herein as the anode-cathode space). The anode includes a plurality of small resonant cavities which are sized according to the desired operating wavelength. A mechanism is provided for constraining the plurality of resonant cavities to operate in what is known as a pi-mode. Specifically, each resonant cavity is constrained to oscillate pi-radians out of phase with the resonant cavities immediately adjacent thereto. An output coupler or coupler array is provided to couple optical radiation away from the resonant cavities in order to deliver useful output power.
The present invention also provides a number of suitable methods for producing such an optical magnetron. Such methods involve the production of a very large number of resonant cavities along a wall of the anode defining the anode-cathode space. The resonant cavities are formed, for example, using photolithographic and/or micromachining techniques commonly used in the production of various semiconductor devices. A given anode may include tens of thousands, hundreds of thousands, or even millions of resonant cavities based on such techniques. By constraining the resonant cavities to oscillate in a pi-mode, it is possible to develop power levels and efficiencies comparable to conventional magnetrons.
According to one particular aspect of the invention, an optical magnetron is provided. The optical magnetron includes an anode and a cathode separated by an anode-cathode space; electrical contacts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space; at least one magnet arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field; and a plurality of resonant cavities each having an opening along a surface of the anode which defines the anode-cathode space, whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings of the resonant cavities to create a resonant field in the resonant cavities; wherein the resonant cavities are each designed to resonate at a frequency having a wavelength xcex of approximately 10 microns or less.
According to another aspect of the invention, an optical magnetron is provide which includes a cylindrical cathode having a radius rc; an annular-shaped anode having a radius ra and coaxially aligned with the cathode to define an anode-cathode space having a width wa=raxe2x88x92rc; electrical contacts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space; at least one magnet arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field; and a plurality of resonant cavities each having an opening along a surface of the anode which defines the anode-cathode space, whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings of the resonant cavities to create a resonant field in the resonant cavities; wherein the resonant cavities are each designed to resonate at a frequency having a wavelength xcex, and a circumference 2xcfx80ra of the surface of the anode is greater than xcex.
In accordance with still another aspect of the invention, an optical magnetron includes an anode and a cathode separated by an anode-cathode space; electrical contacts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space; at least one magnet arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field; and a high-density array of N resonant cavities formed along a surface of the anode which defines the anode-cathode space, each of the N resonant cavities having an opening whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings of the resonant cavities to create a resonant field in the resonant cavities; wherein N is an integer greater than 1000.
In yet another aspect of the invention, a magnetron, includes an anode and a cathode separated by an anode-cathode space; electrical contacts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space; at least one magnet arranged to provide a dc magnetic field within the anode-cathode space generally normal to the electric field; a plurality of resonant cavities each having an opening along a surface of the anode which defines the anode-cathode space, whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings of the resonant cavities to create a resonant field in the resonant cavities; a common resonator around an outer circumference of the anode to which at least some of the plurality of resonant cavities are coupled to induce pi-mode operation.
According to still another aspect, a magnetron is provided which includes an anode and a cathode separated by an anode-cathode space; electrical contracts for applying a dc voltage between the anode and the cathode and establishing an electric field across the anode-cathode space; a pair of magnets arranged at opposite ends of the anode to provide a dc magnetic field within the anode-cathode space generally normal to the electric field; and a plurality of resonant cavities each having an opening along a surface of the anode which defines the anode-cathode space, whereby electrons emitted from the cathode are influenced by the electric and magnetic fields to follow a path through the anode-cathode space and pass in close proximity to the openings of the resonant cavities to create a resonant field in the resonant cavities; wherein the anode comprises at lease an upper anode and a lower anode, the resonant cavities of the upper anode are each designed to resonate at a frequency having a first wavelength and resonant cavities of the lower anode are each designed to resonate at a frequency having a second wavelength different from the first wavelength.
In yet another aspect, a method of forming an anode for an optical magnetron is provided. The method includes the steps of forming a photoresist layer around an outer surface of a cylindrical core made of a first material; patterning and etching the photoresist layer to form a plurality of vanes which extend radially from the outer surface of the cylindrical core to define a plurality of slots; plating the cylindrical core and vanes with a second material different from the photoresist and the first material; and removing the vanes and cylindrical core from the plating to produce a cylindrical anode having a plurality of slots.
According to still another aspect, a method of forming an anode for an optical magnetron is provided. The method includes the steps of forming a layer of material from which the anode is to be made; patterning and etching the layer to form a first layer of a cylindrical anode with a plurality of resonant cavities formed along an inner circumference of the anode; forming at least one subsequent layer of material and repeating the step of patterning and etching in order to increase the vertical height of the anode.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.